Biodiversity and Conservation

, Volume 21, Issue 14, pp 3711–3727

Bat diversity in the lowland forests of the Heart of Borneo

Authors

    • School of Anthropology and Conservation, Durrell Institute of Conservation and Ecology, University of Kent
    • School of Biological and Chemical Sciences, Queen Mary University of London
  • Monika Bożek
    • Genome Centre, John Vane Science Centre, Charterhouse SquareQueen Mary University of London
  • Jan Hildebrand
    • School of Biological and Chemical Sciences, Queen Mary University of London
  • Stephen J. Rossiter
    • School of Biological and Chemical Sciences, Queen Mary University of London
  • David J. W. Lane
    • Department of BiologyUniversiti Brunei Darussalam
Original Paper

DOI: 10.1007/s10531-012-0393-0

Cite this article as:
Struebig, M.J., Bożek, M., Hildebrand, J. et al. Biodivers Conserv (2012) 21: 3711. doi:10.1007/s10531-012-0393-0

Abstract

Borneo’s rainforests are renowned for their high levels of biodiversity, yet information on the distribution and structure of this diversity is lacking, particularly for less charismatic taxonomic groups. We quantified bat diversity across ten sites within a contiguous tract of largely undisturbed rainforest in the Heart of Borneo (HoB) transboundary conservation area. Using comparative analyses of 1,362 bat captures from six sites in Brunei Darussalam, together with data from four additional sites in neighbouring territories, we show that the main differences in bat assemblage composition between sites were driven by the abundances of a few cave-roosting species. Beta diversity (distance decay) was notably low and non-significant. Bat assemblage structure in these undisturbed palaeotropical forests is therefore relatively homogenous in the absence of environmental gradients. By adding 15 bat species to the Brunei national inventory, we confirm the area of north Borneo to be species-diverse and therefore a priority for conservation efforts. However, we also highlight that coastal forest to be included in a recent extension to the HoB hosts bat assemblages with the fewest species and lowest densities. We maintain that extending the HoB in Brunei to include a more diverse portfolio of habitat types is still warranted on the grounds of maximising botanical diversity and habitat area, as long as it does not detract attention from interior forests that support higher vertebrate diversity.

Keywords

ChiropteraBruneiBeta diversityDistance decayTropical forestConservation

Introduction

The tropical rainforests of Borneo are globally recognised for their high levels of species diversity and endemism, forming part of the Sundaic hotspot of Southeast Asia (Sodhi et al. 2004). At least 288 terrestrial mammals (Payne et al. 2000) are reported, of which 44 are endemic (Mackinnon et al. 1996). Mammal diversity and endemism appear to match patterns of other taxonomic groups, with diversity greatest in the north of the island within the states of northern East Kalimantan (Indonesia), Sabah and eastern Sarawak (Malaysia), and the sultanate of Brunei Darussalam (Catullo et al. 2008; Mackinnon et al. 1996). Although this pattern might in part be due to historical biases in reporting, it has also received support from recent island-wide analyses of species distributions (Beck et al. 2011; Meijaard and Nijman 2003; Raes et al. 2009). Unfortunately, the region of northern Borneo is also undergoing high levels of habitat loss; unsustainable logging practices and clearance of rainforest for plantation agriculture are of particular conservation concern (Fitzherbert et al. 2008).

In a bid to safeguard Borneo’s biodiversity the governments of Brunei, Indonesia and Malaysia recently signed a declaration to conserve 22 million ha of continuous habitat within a transboundary conservation area known as the Heart of Borneo (HoB) (WWF 2011). The proposed area was designed to maintain the forests of greatest landscape connectivity, ecosystem service, and importance for the island’s charismatic megafauna. To meet these targets more effectively there have been recent calls to extend the area to include additional lowland forests along Borneo’s northern coast. However, very little is known of the diversity and distributions of much of the wildlife within the HoB, and the proposed extension, and this is particularly true for less charismatic groups such as small mammals and bats.

Bats are a highly diverse animal group and, like other vertebrates, form a centre of richness in the Indo-Malayan region (Findley 1993). In the palaeotropics bats form a major component of forest fauna, and in Borneo comprise at least 93 species representing a third of terrestrial mammals (Payne et al. 2000). Palaeotropical bat assemblages are typically dominated by insectivorous species of the families Hipposideridae and Rhinolophidae, as well as the Vespertilionidae subfamilies Kerivoulinae and Murininae (Furey et al. 2010; Kingston et al. 2003). These species are highly adapted for foraging in forest-interior habitats, and form clear and predictable ensembles based on their ecomorphological traits (e.g. wing loading, aspect ratio and echolocation signal design; Kingston et al. 2003) and roosting ecology (e.g. foliage, tree cavities, caves; Struebig et al. 2008). However, such specialised characters and lifestyles mean that many forest-interior bat species are, in consequence, particularly susceptible to habitat disturbance. Bat assemblages undergo structural changes following habitat degradation (Furey et al. 2010), and lose species following forest fragmentation (Struebig et al. 2008, 2011) and conversion (Phommexay et al. 2011). Should these trends continue, up to forty percent of Southeast Asia’s bats are predicted to become regionally extinct by 2100 (Lane et al. 2006).

Some of the first research on palaeotropical bat assemblages was undertaken on Borneo (Francis 1990, 1994), but there has been remarkably little research on the island since. Of the few studies that have been undertaken, most have focused on single site inventories. For example, bat diversity estimates are highest for Kabili-Sepilok Forest Reserve in Sabah (41 species; Francis 1990, 1994) and Ulu Temburong National Park in Brunei (35 species; Kofron 2002). Unsurprisingly, diversity estimates are greater where sampling was extended to multiple sites within an area (e.g. 44 species in Kinabalu National Park; Yasuma and Andau 2000). Nevertheless, aside from site inventories we still know very little about how bat assemblages are structured over the forested landscape of Borneo, and elsewhere in the palaeotropics.

As part of a broader survey programme on Borneo, we undertook bat surveys in Brunei Darussalam at sites within a 380,000 ha tract of mostly undisturbed forest, covering the main geological formations in north Borneo and elsewhere in the HoB. Historical bat survey records in this area are limited to fruit bats and easily-captured insectivorous species (Kofron 2002; Struebig et al. 2010; Yasuma and Abdullah 1997). Sampling in this region provided us with the opportunity to study assemblage patterns in a near-pristine ecosystem, while also informing the conservation mission of the HoB initiative.

Species composition can be randomly aggregated according to neutral variation in dispersal and ecological drift, and/or governed by variation in other factors such as local habitat conditions (Chase 2005). Therefore, to separate these potential influences, we examined spatial turnover in bat assemblages between sites in the undisturbed forest by testing for decay in assemblage similarity with geographic distance. Distance decay describes the tendency for assemblages to be spatially correlated, whereby nearby sites are biologically more similar than those further away (Soininen et al. 2007). If assemblage similarity is dictated by neutral historical influences, and less so by environmental heterogeneity (such as that presented by habitat differences between sites), then a decay in similarity with distance is expected.

Methods

Study sites

Bat sampling was undertaken at six forested sites in Brunei that represent the main geological formations of north Borneo. Sites were selected to improve existing inventories (at Andulau, Tasek Merimbun and Ulu Temburong) or to provide new data from un-surveyed areas (Peradayan, Bukit Teraja and Sungai Ingei) (Fig. 1; Table 1). All sites are connected by continuous lowland rainforest and bat surveys were undertaken in the dominant vegetation formation, mixed dipterocarp forest (MDF). Under-surveyed sites were identified by mapping all bat species locality records from the literature as well as from specimen records from Brunei Museums department (Kofron 2002; Struebig et al. 2010; Yasuma and Abdullah 1997; Fig. 1).
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Fig. 1

Locality records of bat species in Brunei Darussalam, north Borneo, according to Brunei Museums records, the literature, and this study. Point size is proportional to the number of bat species reported from a site (i.e. site richness; range 1–30 species). All 61 localities (310 records) are at least 1 km apart. The six sampling sites from this study are indicated in large bold type, and four additional sites used for beta diversity analyses are shown in the inset (DV Danum Valley, KS Kabili-Sepilok, LB Loagan Bunut, MB Maliau Basin). Forest cover according to Miettinen et al. (2011) is indicated by grey shading (lowland, grey and upland, dark grey); major rivers are shown just for Brunei. The location of Brunei Darussalam (dark grey shading) is shown relative to the Heart of Borneo area (light grey shading) and other Borneo states in the inset

Table 1

Protection status, geological features and bat assemblage characteristics of sites surveyed in Brunei Darussalam during 2009 and 2010

Site, protection status

Soils

Rock strata

Trap nights

na

Catch rateb

Sc

E1/Dd

1. Andulau, forest reserve 4°39′N, 114°31′E

Infertile yellow sandy latosols

Soft sandstone/clay

50

108

2.2

20

0.72

2. Tasek Merimbun, heritage park 4°35′N, 114°40′E

Clay lithosols

Thick clay/shale

50

119

2.4

15

0.67

3. Bukit Teraja, protection forest 4°18 N, 114°25 E

Clay lithosols

Thick clay/shale

11

124

11.3

15

0.15

4. Sungai Ingei, conservation forest 4°90′ N, 114°42′ E

Yellow podsols

Soft sandstone

20

531

26.6

22*

0.32

5. Peradayan, forest reserve 4°45′ N, 115°10′ E

Shallow immature podsols

Hard sandstone ridge outcrops

16

319

19.9

20

0.15

6. Ulu Temburong, national park 4°32′ N, 115°12′ E

Yellow clay latosols

Shale and clay

59

141

2.4

22

0.52

Geological information is based on Ashton (2010) and Ashton et al. (2003)

aNumber of individual bats captured in harp traps

bMean number of bats captured per trap

cTotal number of species captured in harp traps. Further species were captured in mist nets at some sites (see Table 2 and Supplementary Materials for full inventories)

dSimpson evenness at a common sample size of 96 individuals derived by rarefaction. Values are calculated by the formula E = (1/D)/S when D is Simpson diversity and S is richness (both rarefied to common sample size)

While study sites were all of the same broad forest type (MDF), they varied substantially in their geology, and hence the potential for supporting bat species dependent on formations such as caves (Table 1). Two of the forests were associated with nutrient poor soils with a notable absence of cave or boulder formations. The first was Andulau Forest Reserve, which is one of the last remaining areas of a unique forest assemblage growing on yellow-sandy soils, and which is considered botanically ‘hyperdiverse’ by Ashton (2010). We surveyed an undisturbed area in the vicinity of Ashton’s original botanical plots, described in Sukri et al. (2011). The second site was within Tasek Merimbun Heritage Park in Tutong district, which encompasses 7,800 ha. Bat surveys here were undertaken along low-lying fringes of otherwise poorly drained peat soils. The fringes encompass a substantial area and are characterised by clay lithosols rather than the sandy soils described by Ashton (2010).

The remaining four sites were geologically distinct from Andulau and Merimbun. Ulu Temburong National Park encompasses hilly terrain of approximately 50,000 ha in the Batu Apoi Forest Reserve in Temburong district, and is characterised by dark grey shale with occasional layers of sandstone and limestone (Sukri et al. 2011). We sampled bats along the east ridge of Kuala Belalong Field Studies Centre, which has the largest bat inventory recorded from Brunei (Kofron 2002; Struebig et al. 2010). Peradayan Forest Reserve is near to Ulu Temburong, but is characterised by podsol soils, hard sandstone ridges and boulder formations. Although the reserve has been selectively logged in parts, the majority remains intact. Within the Peradayan Reserve bats were sampled at Bukit Patoi, an unlogged area of 1,027 ha. Sungei Ingei Conservation Forest remains a remote outpost of Brunei at the headwaters of the Belait river. This site is characterised by soft sandstone with some boulder formations leading to steep hills near the Sarawak border. Bat surveys were undertaken along national border patrol trails within 5 km of a temporary base-camp established by Brunei Museums department. The sixth site, Bukit Teraja, lies within 6800 ha of protected forest in Belait district and, unlike the previous three sites, is characterised by thick clay and shale, with some boulder formations. Surveys were undertaken along border patrol trails near the Teraja waterfall.

Bat capture and identification

Bats were captured in four-bank harp traps (Muzeum Zoologicum Bogoriense, Cibenong, Indonesia) using a standardised protocol successfully employed on Borneo and elsewhere in Southeast Asia (Kingston et al. 2003; Rossiter et al. 2012; Struebig et al. 2010, 2011). Traps were positioned across trails and streams each night, approximately 50 m apart, and checked in the evening and following morning within 2 h following dusk and dawn. Each trap was set for one night and then moved to a new position the following day to minimise trap shyness and to give a fully standardised trapping unit across nights. Between three and seven traps were set each night depending on the logistical demands of the survey. In Southeast Asia harp traps are most effective at capturing the insectivorous bats that forage in the forest-interior (sensu Kingston et al. 2003), and so this group of bats were the subject of subsequent analyses. Mist nets (70 denier nylon, four shelves, 30 mm mesh size, Ecotone, Gdynia, Poland) were set over rivers or streams at two sites (Ingei and Merimbun) to supplement bat inventories, but capture data were not included in analyses because of well-documented variation in capture success between traps and nets (Kingston et al. 2003). Bat surveys were undertaken in the dryer seasons of 2009 and 2010 (June to October). Because periods of heavy rain can adversely affect catch rates (Kingston, 2009), trapping in such periods was avoided.

Collected bats were held individually in cloth bags and identified from external characters using a key based on Payne et al. (2000). Standard external data on sex, age and reproductive status as well as morphological measurements (weight; forearm length; tibia length), were obtained before marking each bat on the wing using a 3 mm diameter biopsy punch (Stiefel Laboratories, High Wycombe, UK) so that recaptures could be recognised and removed from analyses. We limited specimen collection to only vouchers of taxa new to the Brunei list or those of taxonomic uncertainty. In total 30 specimens were collected (typically only one or two individuals of a species), stored in 70 % ethanol and deposited in the faunal collection of Brunei Museums department. All other bats were released at the capture point unharmed within 12 h. Live trapping procedures and handling of bats followed guidelines of the American Society of Mammalogists (Sikes et al. 2011).

Site level (alpha) diversity

Because assemblage analyses can be strongly affected by sample size differences between sites, bat diversity at each location was estimated using rarefied species accumulation curves of site abundance data. To account for variation in bat density between sites, we undertook sample-based rarefaction rescaled to individuals in EstimateS (Colwell 2009), and observed site species richness was compared at the lowest common sample size (n = 96). Richness was also compared at a higher common sample size by predicting richness up to the level of the most abundant site (Ingei; n = 472). We used the multinomial model introduced by Shen et al. (2003), implemented in the software SPADE (Chao and Shen 2003–2005), whereby the number of new species recorded after additional sample effort is predicted. Although there are many other estimation or prediction methods available, they frequently become unstable and perform poorly when extrapolating to high sample sizes (Shen et al. 2003). The Shen predictor is relatively stable under these circumstances and has performed favourably when tested against other estimators using harp trap data from elsewhere in Southeast Asia (Kingston 2009). Moreover, we undertook preliminary analyses predicting to a lower sample size and the standard errors associated with the richness predictions were similar. To quantify assemblage evenness, we used the reciprocal form of the Simpson index corrected for species richness (E1/D = (1/D)/S), which is a robust measure of diversity weighted towards the influence of dominant species in the sample. High values therefore indicate even species abundances irrespective of the number of species. This metric was also rarefied to a common sample size in order to reliably compare evenness between sites.

Site similarity and distance decay (beta diversity)

Similarity indices are prone to the same sampling related biases as estimates of alpha diversity, and so to minimise this problem we used frequency-based indices that better account for variation in sample sizes between sites. The Morisita–Horn similarity index is based on the Simpson concentration and so is sensitive to the dominant species of assemblages, which results in undetected species (i.e. those expected to be rare) having little effect on the metric (Chao et al. 2008). Using this index had the added advantage that we were also able to calculate similarity across all sites using a recently developed probabilistic approach (Chao et al. 2008). Chao et al.’s version of the Morisita index estimates similarity for multiple assemblages based on shared information between any two assemblages. Differences in the magnitude of this similarity were assessed using 95 % confidence intervals based on 200 bootstrap replicates. We also repeated pair-wise analyses using a recently modified version of the Jaccard index, which extends this measure of similarity to use abundance data and account for missing species (Chao et al. 2005). Pair-wise similarity matrices were calculated in EstimateS and visualised by presenting data from inventories as an unrooted tree produced by neighbour joining in the software Phylip v3.69 (http://www.phylip.com/).

In order to improve our ability to detect distance decay, we also obtained and included data from four other undisturbed lowland sites in the neighbouring territories of Sabah and Sarawak (Fig. 1). These were Danum Valley Conservation Area (Kingston and Hodgkison 1994), Kabili-Sepilok Forest Reserve (Francis 1990), Loagan Bunut National Park (Gumal et al. 2008) and Maliau Basin Conservation Area (Struebig, Bernard and Turner, Unpublished Data). Crucial to our analyses, all of these inventories were undertaken in relatively undisturbed areas, in the same contiguous forest as the Brunei sites, and used comparable sampling protocols.

To test for distance decay we assessed correlation between the matrices of pair-wise similarity values and those of geographic distances using a Mantel test in Genalex (Peakall and Smouse 2006) with 999 permutations. We also re-tested these distance-matrix correlations using the non-parametric RELATE test in Primer version 5 (Clarke and Warwick 2001), which does not assume linearity.

Results

Assemblage composition

We captured a total of 1,362 individual bats of 35 species at the six Brunei study sites, the majority of which (1,249 bats of 27 species) were forest-interior insectivorous species (Tables 1, 2). The representation of bat families in assemblages varied over the Brunei forested landscape, with vespertilionids of the subfamilies Kerivoulinae and Murininae typically well represented at most sites, and other families (Hipposideridae and Rhinolophidae) being more patchily represented across sites (Table 2; Fig. 2). Nonetheless in terms of total captures, hipposiderid and rhinolophid species that predominantly roost in caves were the most abundant taxa (894 individuals of ten species over the six sites), and hipposiderids in particular contributed the most to high capture rates and low evenness at Ingei, Peradayan and Teraja (Table 1; Fig. 2). Conversely, bats from these families were often present but comparatively rare in the forest of Andulau and Merimbun (Table 2; Fig. 2). Dominant species of this ensemble included Hipposideros cervinus (abundant at Ingei, Peradayan, Temburong and Teraja), and Rhinolophus creaghi (highly abundant at Ingei, and representing the first record of this species in Brunei). Rare cave‐roosting species included H. ater and Megaderma spasma, both of which were only captured once, at Temburong and Peradayan respectively.
Table 2

Bats species reported from the six survey sites in Brunei Darussalam, including the total number of species and individuals captured in this study

Family, speciesa

Foraging strategyd

Roosting ecologye

Andulau

Merimbun

Teraja

Ingei

Peradayan

Temburong

Pteropodidae (fruit bats)

 Aethelops aequalis (alecto)

Bf

T

     

X

 Balionycteris maculata

Bf

T

5

8

1

8

3

2

 Chironax melanocephalus

Bf

T

1

1

    

 Cynopterus brachyotis

Bf

T

 

X

3

2

  

 Cynopterus minutus

Bf

T

     

X

 Dyacopterus spadiceus

Cf

C

     

X

 Eonycteris major

Cf

C

     

X

 Eonycteris spelaea

Cf

C

     

X

 Macroglossus minimus

Bf

T

X

    

X

 Megaerops ecaudatus

Bf

T

X

X

   

X

 Megaerops wetmorei

Bf

T

X

X

   

X

 Penthetor lucasi

Bf/Cf

C

     

X

 Pteropus vampyrus

Cf

T

     

X

 Rousettus amplexicaudatus

Cf

C

 

X

 

X

  

 Rousettus spinalatus*

Cf

C

   

X

  

Emballonuridae (sheath-tailed bats)

 Emballonura alecto

Ei

T

  

X

  

X

 Emballonura monticola

Ei

T

  

1

  

13

Mollosidae (free-tailed bats)

 Cheiromeles torquatus

Oi

C

     

X

 Mops mops

Oi

C

 

X

   

X

Megadermatidae (false vampires)

 Megaderma spasma

Ni

T/C

    

1

 

Nycteridae (hollow-faced bats)

 Nycteris tragata (javanica)

Ni

T

 

1

  

1

1

Hipposideridae (roundleaf bats)

 Hipposideros ater*

Ni

C

     

1

 Hipposideros bicolor

Ni

C

   

5

1

2

 Hipposideros cervinus

Ni

C

  

91

199

266

27

 Hipposideros cineraceus

Ni

C

     

X

 Hipposideros diadema

Ni

C

8

X

4

11

2

3

 Hipposideros doriae

Ni

T

   

2

  

 Hipposideros dyacorum

Ni

C

9

5

  

2

15

 Hipposideros galeritus

Ni

C

   

52

  

 Hipposideros ridleyi

Ni

T

5

13

 

4

3

6

Rhinolophidae (horseshoe bats)

 Rhinolophus borneensis

Ni

C

  

2

11

5

2

 Rhinolophus creaghi*

Ni

C

   

167

  

 Rhinolophus philippinensis

Ni

C

   

X

  

 Rhinolophus sedulus

Ni

T

13

5

1

 

2

10

 Rhinolophus trifoliatus

Ni

T

6

14

1

1

4

3

Verpertilionidae (evening bats)

 Kerivoulinae (woolly bats)

  Kerivoula hardwickii

Ni

T

6

24

1

1

3

1

  Kerivoula intermediab

Ni

T

17

5

1

 

8

10

  Kerivoula lenisc*

Ni

T

5

5

 

1

 

6

  Kerivoula minutab*

Ni

T

4

8

1

15

2

4

  Kerivoula papillosac

Ni

T

9

19

9

4

 

21

  Kerivoula pellucida*

Ni

T

3

2

 

3

1

3

  Kerivoula sp.c*

Ni

T

1

5

2

10

9

4

  Kerivoula whiteheadi

Ni

T

X

X

    

  Phoniscus atrox *

Ni

T

   

1

 

1

  Phoniscus jagorii*

Ni

T

1

     

Murininae (tube-nosed bats)

 Murina aenea*

Ni

T

1

 

1

   

 Murina cyclotis

Ni

T

 

X

 

1

 

5

 Murina rozendaali*

Ni

T

1

     

 Murina suilla*

Ni

T

7

4

1

4

 

1

Vespertilioninae (evening bats)

 Glischropus tylopus

Ei

T

5

 

4

28

2

 

 Myotis ater*

Ei

C/T

    

1

 

 Myotis muricola

Ei

T

1

X

  

1

X

 Myotis ridleyi

Ei

T

   

1

2

X

 Pipistrellus tenuis

Ei

C/T

 

X

    

 Hypsugo (Pipistrellus) vordermanni

Ei

C/T

     

X

Total bats species reported:

  

23

25

17

25

20

39

Additional species captured in mist-nets in this study or reported elsewhere in the literature are indicated by X. New additions to the Brunei Darussalam bat species inventory are indicated by asterisks. Previous nomenclature for species are indicated by parentheses

aNomenclature follows Simmons (2005). Older species names used in Payne et al. (2000) are listed in parentheses following the species name

bKerivoula intermedia and minuta are difficult to distinguish in the hand and were therefore separated by body mass (K. intermedia > 2.75 g; range: 2.75–4.0 g; K. minuta < 2.5 g; range: 2.0–2.5 g)

cBats historically defined as Kerivoula papillosa exhibit extensive morphological variation on Borneo and elsewhere in Southeast Asia, and so the concept of K. papillosa includes multiple species (Khan et al. 2010). We defined three taxa separated by forearm length, examples of which were later confirmed as distinct taxa by genetic barcodes. K. lenis < 40 mm; K. papillosa 40-44 mm; Kerivoula spp. > 45 mm. The molecular systematics of this species complex is under ongoing investigation

dForaging strategies assigned based on wing morphology (Kingston et al. 2003; Struebig et al., 2010): Bf, frugivorous or nectarivorous species that forage in clutter below the forest canopy; Of, frugivorous or nectarivorous species that forage in open areas and over large distances; Ei, insectivorous species that forage in partially cluttered edges and/or canopy edges; Oi, insectivorous species that forage in open areas and over large distances; Ni, forest-interior insectivorous species that typically forage in narrow-spaces or clutter (although they may commute some distance to foraging sites). Foraging strategies are used in combination with roosting ecology to assign species to ensembles

eThe main roost structures reported in the literature and by personal observations for each bat species (Kofron, 2002; Payne et al. 2000; Struebig et al., 2010; Yasuma and Andau, 2000): T, ephemeral roosts in trees, hollows or other foliage; C, caves, boulders, houses. Roosting ecology is used in combination with foraging strategies to assign species to ensembles. When two categories are listed the first the predominant observation from the literature

https://static-content.springer.com/image/art%3A10.1007%2Fs10531-012-0393-0/MediaObjects/10531_2012_393_Fig2_HTML.gif
Fig. 2

Abundance per unit effort of the main bat families (Rhinolophidae, Pteropodidae, Hipposideridae) and sub-families (Murininae, Kerivoulinae, Vespertilioninae) captured in harp-trap inventories of the six Brunei sites. Open bars indicate that capture rates exceeded 4.0 bats per trap

Tree cavity/foliage-roosting species represented a lower proportion of overall captures (375 bats; 18 species), but were more uniformly distributed across sites (Table 2; Fig. 2). Dominant species of this ensemble included Kerivoula papillosa, K. minuta and K. intermedia, which were well represented at most sites surveyed. Rare species included Murina rozendaali and Phoniscus jagorii (both singletons, recorded from a single capture each in Andulau for the first time in Brunei), as well as P. atrox, Murina aenea and H. doriae, which were recorded by only two captures each. Pooling forest-interior bat capture data from the six sites generated a species accumulation curve that had clearly passed the point of inflection and approached an asymptote, suggesting that the majority of bat species of this ensemble had been captured. (Fig. 3a).
https://static-content.springer.com/image/art%3A10.1007%2Fs10531-012-0393-0/MediaObjects/10531_2012_393_Fig3_HTML.gif
Fig. 3

Species accumulation and richness of forest-interior insectivorous bats sampled at six forest sites in Brunei. Accumulation curve and singletons curve for all sites combined (a), and accumulation curves for sites independently (b) are derived by sample-based rarefaction re-scaled to individuals. Comparisons of richness are made at the lowest common sample size (c), and also at the sample size of Sungai Ingei, the site with the greatest number of individuals captured (d). Error bars (c, d) indicate the 95 % confidence limits of mean diversity derived from rarefaction (c, sensu Colwell 2009) or prediction (d, sensu Shen et al. 2003) at n individuals. Values falling outside of the confidence limits of other sites are significantly different. Open circles on c and d indicate the observed richness (i.e. non-rarefied) of all captured forest-interior bats

Alpha diversity

When species richness estimates were rarefied down to a common sample size, Andulau and Temburong were ranked as sites with the most bat species (Fig. 3b, c), hosting significantly more species than Ingei, Peradayan and Teraja. However, when accounting for species not yet recorded in inventories (using the Shen multinomial predictor), Andulau was outranked by Ingei, Temburong and Teraja, supporting significantly fewer species than the latter two sites (Fig. 3d). Contrary to expectations, Merimbun supported the fewest predicted bat species overall (12‐13 species; Fig. 3d), but together with Andulau and Temburong exhibited high species evenness (Table 1). Notably, the Teraja inventory exhibited low richness and evenness (Table 1), resulting in a species accumulation curve that intersected those of other sites, thus indicating that more species may actually be present than our sampling uncovered and that diversity comparisons with this curve should be interpreted with caution.

Beta diversity

Overall similarity in bat species composition was low to moderate (Chao‐Morisita similarity amongst Brunei sites = 0.422 ± 0.014 SE; all ten sites, 0.529 ± 0.012) indicating that at least some species were poorly represented across all of the sites studied. Pair-wise dissimilarity coefficients revealed two patterns of interest reflected by branches in our unrooted tree that were highly differentiated from each other in terms of assemblage composition (Fig. 4). The two nutrient poor forests sampled in Brunei (Andulau and Merimbun) supported similar bat assemblages to each other and also to that of Bunut, another nutrient poor forest area, reflecting the even abundance distribution of tree cavity/foliage-roosting species of the vespertilionid subfamilies Kerivoulinae and Murininae (Fig. 2a, b). A second branch was represented by the Brunei sites Ingei, Peradayan and Teraja, as well as Danum and Sepilok in Sabah; all dominated by the cave‐roosting species, H. cervinus. In fact Peradayan and Teraja, which were characterised by boulder formations, supported near‐identical bat assemblages (Morisita similarity = 0.99). The Temburong assemblage was intermediate between these two groupings, hosting the majority of species from the other sites but at more even abundances. When the nutrient poor sites were removed from analysis, overall similarity amongst sites was significantly greater (for Brunei, 0.687 (CI: 0.631–0.743); including other sites, 0.656 (CI: 0.622–0.689).
https://static-content.springer.com/image/art%3A10.1007%2Fs10531-012-0393-0/MediaObjects/10531_2012_393_Fig4_HTML.gif
Fig. 4

Unrooted tree showing similarity of forest-interior insectivorous bat assemblages at 10 forested sites in northern Borneo (Brunei, Sabah, and Sarawak) based on the Morisita similarity index. Two main branch clusters are evident: the nutrient poor forests of Andulau and Merimbun, as well as Bunut, host similar assemblages (dominated by tree/cavity-roosting bat species), as do Ingei, Teraja and Peradayan in Brunei, and Danum and Sepilok in Sabah (dominated by cave-roosting bat species). Temburong, the most species diverse assemblage overall, is intermediate between the two clusters. The six Brunei sites sampled during this study are in bold black type; additional sites from Sabah and Sarawak are shown in grey italics

Mantel and RELATE tests did not reveal evidence of distance decay, suggesting that assemblage structure was poorly influenced by neutral processes at the spatial scale of our study. Assemblage dissimilarity was not significantly correlated with geographic distance whether determined by Morisita coefficients (RMANTEL2 = 0.018, P = 0.177; RhoRELATE = −0.233, P = 0.083) or Chao-Jaccard coefficients (RMANTEL2 = 0.039, P = 0.116; RhoRELATE = −0.207, P = 0.058). This finding was consistent when geographic distances were log-transformed and similarity coefficients calculated on square-root transformed abundance data to reduce the skew of highly abundant species.

Discussion

Our bat surveys in 380,000 ha of largely undisturbed Bornean rainforest revealed substantial diversity and subtle differences in assemblage composition between sites. We recorded 35 bat species at six sites in Brunei, which added 15 more species to the national species list (see Supplementary Material). Of these 35 species, 27 were insectivorous forest-interior specialists. A species accumulation curve summarising assemblage data from these six sites suggested that the landscape-scale inventory for forest-interior bats was near-complete. Indeed the Borneo-wide total for this foraging group is in the region of 35 species (Struebig et al. 2010). The presence of four singletons in the Brunei inventory (Fig. 3a), and the presence of three taxa reported as singletons in the four inventories used for distance decay analyses, indicates that forest-interior bat species remaining to be uncovered in the Brunei region are likely to be rare. On the other hand, there are a substantial number of vespertilionids known from other forested areas on Borneo that were not well represented in the Brunei inventory (particularly pipistrelles, Tylonycteris and Hesperoptenus species). These bats, of which there at least 20 reported from Borneo, are known to forage around edges, canopies and open spaces, and are typically difficult to capture with harp traps. Therefore underrepresentation in our inventories does not necessarily infer rarity. In order to sample these species effectively future surveys would benefit from acoustic monitoring techniques and mist-netting over water bodies.

The pattern of bat assemblage composition across north Borneo’s forested landscape was mostly driven by distinct assemblages at a small number of sites. Relatively depauperate bat assemblages in nutrient-poor forests contributed substantially to the signal of landscape-wide beta diversity, and when these sites were removed from analyses the similarity in bat species composition across the forested landscape was notably greater. While Andulau and Merimbun were predicted to support moderate numbers of forest-interior bat species (13–18 according to Shen multinomial predictions), the observed species composition was typically a subset of otherwise richer sites further inland. Two tree cavity/foliage-roosting species (Murina rozendaali and Phoniscus jagorii) found at the nutrient poor sites during our study were notably rarely captured and are only known from a handful of records on Borneo (Struebig et al. 2010), but we believe it likely that further surveys would reveal these species in forests elsewhere in the region. On the other hand, locality records from this study and elsewhere on Borneo (Struebig et al. 2010) suggest that another species (Kerivoula whiteheadi) could be largely restricted to such habitat, as all confirmed records are from forests on peat or sandy soils. The main differences in species composition between sites were driven by the presence or absence of dominant cave-roosting species (e.g. Hipposideros cervinus). The proximity of a bat survey to major roosting sites can have a strong bearing on the assemblage composition described, with the dominance of cave-roosting species detectable several kilometres away from a large bat roost (Struebig et al. 2009). Once these species are recognised and accounted for in assemblage analyses—for example by transforming species abundances or by removing selected species (McCune and Grace 2002)—bat assemblage composition in undisturbed palaeotropical forests, at least in Borneo, would appear relatively homogenous in the absence of environmental gradients.

Our inability to detect a significant pattern of distance decay between assemblage similarity and geographic distance supports the idea that, at the spatial scale studied here, the neutral processes of ecological drift and differential dispersal capabilities do not have a major role in shaping bat assemblages in the undisturbed forests on Borneo. This is in contrast with the findings from Bornean moths (Beck and Khen 2007) and butterflies (Cleary and Genner 2006), for which assemblage composition appears to be partly influenced by geographical distance. Notably, much of the distance decay detected by these studies was observed over short geographic distances (<20 km), which were not well covered in our study. However, in a previous study of assemblage similarity over comparable geographic distances in peninsular Malaysia, bat assemblages also exhibited little differentiation (Struebig et al. 2011). Together with the results of this study this finding suggests that the dispersal limitations expected to shape beta diversity are not strong enough to significantly influence palaeotropical bat assemblages in continuous habitat, at least across the distances examined (ca. 500 km). It has recently been suggested that low beta diversity (and hence weak distance decay) could be generally expected for tropical taxa, particularly those in homogeneous rainforest habitats with weak gradients in climatic, altitudinal and geological characteristics (Novotny et al. 2007).

The homogeneity of bat species composition in undisturbed continuous habitat indicates that historical processes can be largely discounted from shaping assemblages, and thus structural differences between assemblages may be reliably attributed to other processes such as those associated with habitat disturbance. This is particularly relevant when identifying undisturbed ‘controls’ for studying the impact of environmental change on this animal group. Our results therefore confirm the validity of recent studies that have compared bat assemblages in disturbed habitats with those in such undisturbed controls (e.g. Furey et al. 2010; Phommexay et al. 2011; Struebig et al. 2008, 2011).

The north of Borneo is a species-diverse region and therefore a priority area for conservation efforts. Our findings lend strong support for improving the conservation status of Brunei’s inland forests, which otherwise remain inadequately protected. The inland forests of Brunei and eastern Sarawak support some of the most diverse bat assemblages on Borneo and are comparable in assemblage structure to well-known forest sites in Sabah (e.g. Danum Valley, Maliau Basin, as shown here). For example, the forests of Sungai Ingei host a particularly diverse bat community that includes several species not yet reported from elsewhere in Brunei and only patchily distributed on Borneo (Rhinolophus creaghi, R. acuminatus, and Rousettus spinalatus). On a national level this area is of high conservation priority based on faunal richness. In addition, homogeneity of bat assemblage structure over the extensive forest area in this study suggests substantial interconnectedness among sites, thus indicating that a large forest area should be conserved to maintain natural ecological processes. Although our species inventory for one of the inland sites (Teraja) was notably low, the low evenness and lack of inflection on the species accumulation curve suggests that substantially more species remain to be uncovered and so bat diversity is likely to be comparable to other inland sites. Conversely, we also show that the largely coastal, nutrient-poor forests of Brunei (Andulau and Merimbun) and Sarawak (Bunut) host relatively depauperate bat assemblages. These forests support a number of rare and threatened species (Murina rozendaali, M. aenea and Hipposideros ridleyi; all classified as Vulnerable (IUCN 2011), but overall bat diversity is low with bat species composition similar to peat swamps and heath forests elsewhere on Borneo (Struebig et al. 2006).

Our findings are particularly timely given calls to extend the HoB area to the coastal region of Brunei so that botanically ‘hyperdiverse’ forests can be better represented in the conservation area. These forests are clearly a rare habitat-type: they support the highest levels of tree diversity found in the palaeotropics, appear to be unique to the north and west of Borneo (Ashton 2010), and, following decades of clearance and fragmentation, they now have their largest remnants in Brunei and eastern Sarawak. However, we show that botanical hyperdiversity does not necessarily support high levels of faunal richness. It remains to be seen whether the patterns of bat diversity we describe in these forests is matched by similar trends in other animal groups, though we note that the accessibility of coastal habitats makes them particularly susceptible to disturbance and high hunting pressure. Indeed, other botanically hyperdiverse parks are being rapidly depleted of vertebrates (e.g. Lambir National Park in Sarawak, Harrison 2011). Broadening the geographic scope of the HoB is clearly warranted to improve botanical representation and the protection of a larger habitat area. However such proposals should not detract attention from intact interior forests that are associated with high levels of faunal diversity.

Acknowledgments

The bulk of this work was supported by a Universiti Brunei Darussalam (UBD) grant awarded to MJS whilst a Research Fellow at the university, with additional support from the Queen Mary University of London (QMUL) Expedition Fund to JH. MJS is particularly grateful to Kamariah Abu Salim and the UBD Research Committee for approving the research. During this project we were grateful to the help of many individuals from UBD, Brunei Museums, Forestry Department and local communities. We are particularly grateful to Hj Saidin Bin Salleh, Director of Forestry and Bantong Bin Antaran, Director of Brunei Museums, for granting us permission to access research sites, and to Siti Norhayatty Morni for facilitating access. Special thanks go to Joe Charles, Ang Bee Biaw and Samhan Nyawa, organisers of the Sungai Ingei Faunal Expedition (2010–2012), which was sponsored by Standard Chartered Bank and supported by the Ministry of Industry & Primary Resources, UBD and the World Wide Fund for Nature. Finally we would like to thank Farah Anie, Ulmar Grafe, Caroline Schőner and Michael Schőner, staff of Tasek Merimbun and Kuala Belalong Field Studies Centre for helping with and facilitating fieldwork, as well as the students of the QMUL Tropical Ecology field-courses, for assisting MJS at Tasek Merimbun.

Supplementary material

10531_2012_393_MOESM1_ESM.doc (166 kb)
Supplementary material 1 (DOC 166 kb)

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© Springer Science+Business Media Dordrecht 2012